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Abstract

In single particle spectroscopy, the degree of observed fluorescence anti-bunching in a second-order cross correlation experiment is indicative of its bi-exciton quantum yield and whether or not a particle is well isolated. Advances in quantum dot synthesis have produced single particles with bi-exciton quantum yields approaching unity. Consequently, this creates uncertainty as to whether a particle has a high bi-exciton quantum yield or if it exists as a cluster. We report on a time-gated anti-bunching technique capable of determining the relative contributions of both multi-exciton emission and clustering effects. In this way, we can now unambiguously determine if a particle is single. Additionally, this time-gated anti-bunching approach provides an accurate way for the determination of bi-exciton lifetime with minimal contribution from higher order multi-exciton states.

Due to very high QBX, then second g-NQD shows a bi-exponential decay even at very low pump power. The fast time constant of the PL decay 23.78 ns is in good agreement with 22.9ns τBX extracted from the decay of RTG.”

Other (2)

Due to very high QBX, then second g-NQD shows a bi-exponential decay even at very low pump power. The fast time constant of the PL decay 23.78 ns is in good agreement with 22.9ns τBX extracted from the decay of RTG.”

Figures (3)

Schematic of TCSPC implementations. (a) TCSPC setup allowing for hardware-implemented time-gating. (b) TCSPC setup allowing for software-implemented time-gating. (c) Details of TCSPC calculations. Photon arrival times are indicated by red circles while laser pulses are denoted by blue stars. PL lifetimes are determined by histogramming t values. Time-gating is implemented by using only photons arriving within the time-gated region, depicted by the yellow boxes. The gate-delay time (GDT) is also indicated. Anti-bunching plots are built up by histogramming the time differences, ΔT, between photons arriving on opposing channels.

Single NQD data. Panels (a)-(d) and (e)-(h) correspond to different measurements/data sets. (a) PL lifetime from a single detector channel. Dash line: single exponential fit with time constant of 124 ns. (b) Standard g(2) plot before time-gating. R = 0.50 (c) Plot of RTG vs. GDT. Notice that the first 25 ns (before t = 0) are flat, this corresponds to the time before the sync pulse, due to the electronic delay in the system as is also seen in all lifetime plots. (d) g(2) plot after time gating has been applied (GDT = 75 ns, RTG(75) = 0.05). Note that most if this is due to cross-talk (sharp central spikes). (e) PL lifetime from a single detector channel. Dash line: double exponential fit with time constant of 23.7 and 110.5 ns. (f) Standard g(2) plot before time-gating. R = 0.73 (g) Plot of RTG as a function of GDT. (h) g(2) plot after time gating has been applied (GDT = 75 ns, RTG(7 5) = 0.13).